Any one ever tried water wetter?
Phil Martin wrote:
> I think that one very important factor has been ignored in this discussion
> so far.
>
> You want your cooling system to do _two_ things that are in some respects at
> odds with one another:
>
> 1) Extract heat from the engine
> 2) Give off heat via the rad
>
> It's clearly true that circulating a greater volume of coolant through the
> engine in a given amount of time will increase the cooling capacity _IF_ the
> temperature of the coolant as it enters the engine is kept constant. Note
> that this breaks down for very high flow rates (where particle speeds reach
> a few hundred miles per hour) where the kinetic energy of the coolant
> particles slamming into the water jacket walls would give up energy to the
> engine block. But realistically, at the temperatures and flow rates you're
> going to see in an engine, this effect can almost certainly be completely
> ignored.
>
> However, it's also clearly true that leaving a given volume of water in the
> rad for a longer time will allow it to cool more. So increasing the flow
> rate through the rad decreases the amount of heat that can be dissipated
> from a given volume of coolant for one cycle through the rad. Of course, if
> the universe is gravitationally closed, then after a few dozen billion
> years, the big crunch is going to drive the temperature in that rad way, way
> up. But in that case, you'd have bigger problems. ;)
>
> So, there are two opposing forces here: the faster the coolant flows through
> the engine, the better able it will be to dissipate heat, and the slower it
> flows through the rad, the cooler it will be when it re-enters the engine.
> Depending on the slopes of these two curves, increasing flow through the
> system as a whole could sometimes increase cooling effectiveness, and
> sometimes decrease effectiveness. There are a lot of inter-related
> variables.
>
> You can't generalize and say that a greater flow rate through the system
> increases or decreases operating temperature, because the cooling
> effectiveness depends on both the flow rate through the engine (more flow
> through engine = better cooling), AND the coolant temperature as it enters
> the engine (more flow through rad = higher engine inlet temperature = worse
> cooling).
>
> Which is why the damn thermostat is in there. The thermostat regulates flow
> through the engine to keep the temperature within a certain range so that
> you don't have to figure all this stuff out for yourself. If the engine's
> consistently running too hot, change the thermostat and flush the system to
> get rid of air pockets and/or whatever gunk might be blocking the cooling
> passages. If it's still running too hot, go with a cooler thermostat. If
> it still can't keep up, you probably need a more effective rad, or the
> engine's out of tune somehow.
>
> Of course, as has been pointed out, if you only drive the car very rarely
> the risk of the thermostat seizing might outweigh the inefficiency that
> results from running without one altogether, so there are no easy answers.
>
> Hope this is worth something,
> --
> Phil Martin pmartin@surgnav.com
> "Who's my cream-puff?"
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